If your talking about the voluntary 25 year rule for urtext/critical editions (1991 and before, soon to be 1992 by January), as long as the original composer died more than 50 years ago and the edition was published before 1992, this is fine. Any prefaces by the editors have to be removed from the edition. Now however if their are things added to the score like fingerings, phrase markings, changes to parts of the music (like Henle) this is NOT an true urtext edition, normal copyright protection applies here.

With critical editions it does not matter if the editor is alive or dead less than 50 years. Our voluntary rule is closely patterned on Germany's Section 70, which sets a term of 25 years from date of publication for such editions (literally "scientific editions" in their law). They are not very clear about the status of editor prefaces and continuo realizations and one sees quite a few complete volumes - prefaces and all - in German digital collections. We take a more conservative view and require that prefaces be omitted, along with any continuo realizations that display some originality. (They often look no more creative than the work of any reasonably competent 2nd year theory student, but not always). So 1992 and before is fair game as long as you keep away from prefaces, fancy realizations, reconstructions, and Henle style tricks (urtext editions with plenty of added fingerings, etc.) Urtext is not the legal term, but more of a marketing one.